Novel peptidomimetic inhibitors of signal transducer and activator of transcription 3 dimerization and biological activity

Abstract

The critical role of signal transducer and activator of transcription 3 (Stat3) in the growth and survival of human tumor cells identifies it as a promising target for cancer drug discovery. We previously identified a Stat3 SH2 domain-binding phosphopeptide, PY*LKTK, and its tripeptide derivatives, PY*L and AY*L (where Y* represents phosphotyrosine), which inhibit Stat3 biochemical activity and biological function. Here, we report novel peptidomimetic compounds based on PY*L (or AY*L) with substitution of the Y-1 residue by benzyl, pyridyl, or pyrazinyl derivatives that are selective and greater than 5-fold more potent in disrupting Stat3 activity in vitro than lead tripeptides. The biological activities of these derivatives mirror that originally observed for peptides. In this context, the representative peptidomimetic ISS 610 with 4-cyanobenzoate substitution inhibits constitutive Stat3 activity in Src-transformed mouse fibroblasts and human breast and lung carcinoma cells. This effect is not evident with the non-phosphorylated counterpart, ISS 610NP, consistent with interaction of peptidomimetics with the SH2 domain of Stat3. Moreover, ISS 610 induces cell growth inhibition and apoptosis of Src-transformed fibroblasts that contain persistently active Stat3. We present the first report of a peptidomimetic approach to design of small-molecule inhibitors of Stat3 that are also among the first examples of disruptors of transcription factor dimerization with the potential for novel cancer therapy.

STAT3 pathway in cancers: Past, present, and future

“…S3I-M2001, an oxazole-based peptidomimetic, can inhibit the growth of tumors in mice with breast cancer. 234,288 Ac-pTyr-Leu-Pro-Gln-Thr-Val-NH2, BP-PM6, BP-PM7, and PMM-172 are all STAT3 inhibitors that target the SH2 domain to reduce constitutive STAT3 phosphorylation in cancer cells such as HNSCC and breast cancer cells. [289][290][291] Non-peptidic small-molecule inhibitors also block STAT3 activation.…”

“…ISS 610, which is based on PY*L, was reported to induce the apoptosis of STAT3‐dependent transformed cancer cells without affecting normal cells. S3I‐M2001, an oxazole‐based peptidomimetic, can inhibit the growth of tumors in mice with breast cancer 234,288 . Ac‐pTyr‐Leu‐Pro‐Gln‐Thr‐Val‐NH2, BP‐PM6, BP‐PM7, and PMM‐172 are all STAT3 inhibitors that target the SH2 domain to reduce constitutive STAT3 phosphorylation in cancer cells such as HNSCC and breast cancer cells 289–291 …”

Crispenes F and G, cis-Clerodane Furanoditerpenoids from Tinospora crispa, Inhibit STAT3 Dimerization

“…A methanol extract of the stem of T. crispa led to the isolation of four clerodane-type furanoditerpene lactones (1−4), an alkaloid (5), three terpenoids (6−8), and a sterol (9). Among the isolated diterpenes, compounds 1 and 2 are new, with a carboxylic acid group at position C-8 as found previously only in crispene C. 25 The known compounds were identified as crispene D (3), 25 columbin (4), 26 N-trans-feruloyltyramine (5), 27 cycloeucalenone (6), 28 β-amyrin (7), 29 lupeol (8), and β-sitosterol (9), by comparison of their spectroscopic data with those reported in the literature and by co-TLC with authentic samples.…”

“…The phosphorylation of the STAT3 protein leads to the formation of a homodimer through the reciprocal binding of the SH2 domain of one monomer to the pTyr-containing PYLKTK sequence of another. This dimeric pSTAT3 acts as a transcription factor by translocating to the nucleus, where it binds to its DNA consensus sequence, thus regulating the transcription of numerous genes critical for the survival and proliferation of cancer cells. , A number of different approaches have been taken to identify novel small molecules as STAT3:STAT3 dimerization inhibitors, including the development of peptides or peptidomimetics that bind to the STAT3 SH2 domain, and small molecules, derived from STAT3 structural information and in silico design, that interact with the key residues within the STAT3 SH2 domain. − A number of plant-derived molecules have also shown potent inhibition of the STAT3 signaling pathway and STAT3 dimerization. − …”

Discovery of Novel Azetidine Amides as Potent Small-Molecule STAT3 Inhibitors

“…Much of the earlier efforts to develop inhibitors of STAT3 focused on targeting the SH2 domain to disrupt the interactions with pTyr-containing binding sites and the STAT3:STAT3 dimerization event. 8,9 These efforts have generated a number of small-molecule inhibitors, [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]35 though the clinical development of these inhibitors has been hampered due to their low potency, unclear mechanisms of inhibition of STAT3 signaling, and pharmacokinetic limitations among others. 27 New methods are required to design unique potent small-molecule binders that can potentially overcome the limitations.…”